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Green Component Could Improve Asphalt and Sealant Mixtures
July 2015

Construction crews may someday use a plant molecule called lignin in their asphalt and sealant mixtures to help roads and roofs hold up better under various weather conditions. It also could make them more environmentally friendly, according to research findings, “Sustainable bitumen”, presented at the 249th National Meeting & Exposition of the American Chemical Society (ACS).

Currently a by-product of crude oil production, bitumen is the main sticky ingredient in asphalt and roof sealants. But oil is a nonrenewable resource. And price fluctuations in the oil market have made it more difficult to get high-quality bitumen, forcing manufacturers to look for alternatives, noted Ted Slaghek, Ph.D., a senior scientist at TNO, a non-profit organization in the Netherlands that develops real-world applications for scientific and technological advances.

“In the long term, we have to move to renewable products that we can harvest every year,” says Dr. Slaghek. “It should be logical to use natural organic raw materials instead of crude oil.”

Dr. Slaghek explains that lignin, unlike oil, is a renewable resource that makes up as much as a third of the dry material in trees, where it keeps out water and binds together other components of plant biomatter, like cellulose. Lignin is also plentiful — and therefore, inexpensive — because it is removed as a waste product during the paper-making process. More than 50 million tons are produced globally as waste each year. Most of this is burned to generate electricity to run the paper mills. Burning lignin is not only wasteful, it releases soot and other pollutants, he said.

Because lignin shares many characteristics with bitumen, it has the potential to become an environmentally friendly additive to help reduce the amount of bitumen needed for construction activities.

As is generally the case with other additives, lignin makes sealants perform even better — but those polymer additives come from petroleum sources, making them just as problematic as bitumen. Dr. Slaghek’s team has developed a number of lignin-bitumen mixtures that make the asphalt harder in warm weather, preventing rutting and adding a few years to a road’s lifespan. “On the other hand, if you have roads where the temperatures tend to be lower, bitumen can become too hard and brittle, increasing the chance that rocks and pebbles will come loose and damage your car,” noted Dr. Slaghek. “We have also developed lignin-bitumen mixtures that keep the bitumen more tacky, so at lower temperatures it’s still a good road.” The mixtures contain differing amounts of unmodified lignin, as well as lignin with various chemical modifications.

The advantages of lignin go far beyond these quality, cost and performance benefits, Dr. Slaghek notes. It’s also safe to handle — and consume. “You might be surprised to learn this, but you’re eating lignin every day if you’re eating vegetables,” he pointed out.

The researchers acknowledge funding provided by ICOPAL B.V., Van Gelder B.V. and the Ministry of Economic Affairs of The Netherlands.

Article reprinted from materials provided by the American Chemical Society (ACS). ##

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